This invention relates primarily to a battery pack suitable for high current discharges, and in particular to a battery pack with a plurality of batteries connected in series and parallel.
Battery pack output current can be increased by increasing the number of batteries connected in parallel, and battery pack output voltage can be increased by increasing the number of batteries connected in series. From this, battery packs used in applications requiring large output, such as bicycles, tools, and automobiles, can increase output by connecting a plurality of batteries in parallel, and again connecting those units in series. Since many batteries are housed in this type of battery pack, a configuration which allows efficient connection of each battery is important. As an implementation of this, a battery pack has been developed with batteries connected by a uniquely structured lead plate (see Japanese patent application HEI 10-308205).
As shown in FIG. 1, the battery pack cited in this disclosure has a lead plate 32 spot welded to connect the end-planes of two rows of batteries 31 lined up side by side. The lead plate 32 is provided with a slit 33 along its center line to allow it to smoothly bend along the center line. Further, interconnect wiring projections 35 are provided along the center of the lead plate 32 to project outward for connection to circuit board 34 when the lead plate 32 is bent along the slit 33. When this lead plate 32 is bent back 180° along the slit 33, the interconnect wiring projections 35 protrude outward as shown in FIG. 2. The protruding interconnect wiring projections 35 are connected to the circuit board thereby joining the batteries 31 to the circuit board.
In the battery pack arrangement shown in FIGS. 1 and 2, lead plate electrical resistance in series with parallel connected batteries becomes significant. This is because openings, such as the slit provided at the center region of the lead plate to make it easy to bend, are connected in series. In a high output battery pack, it is important to reduce electrical resistance as much as possible. This is because high currents result in large losses even with extremely small electrical resistance, and consequently this limits maximum output.
The battery pack shown in FIGS. 1 and 2 has the further drawback that since lead plates connected to the terminals of all the batteries are bent 180° and connected to the circuit board, lead plates and batteries can easily become disconnected during lead plate bending. In addition, a lead plate may not be completely disconnected from a battery, but may be in a tenuous connection and may easily become disconnected causing failure during use. Another troubling drawback is due to the narrow space for the lead plate between opposing battery end-planes. This makes it difficult to confirm lead plate to battery connections and makes it extremely difficult to reconnect lead plates disconnected from battery terminals.
Further, in this battery pack configuration, as the number of parallel connected batteries is increased, the size of the circuit board must be increased. Therefore, this battery pack has the drawback that a design change, which changes the number of batteries, cannot be easily accommodated.
The present invention was developed with the object of avoiding the drawbacks described above. Thus, it is the primary object of the present invention to provide a battery pack which allows connection of a large number of batteries in an extremely low resistance configuration, allows a reliable connection of lead plates to batteries in a manner that will not disconnect, allows easy confirmation of lead plate to battery connection region integrity and efficient lead plate to battery connection, and allows easy accommodation of design changes which change the number of batteries to optimize battery pack configuration for the application.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.